Size- and Support-Dependent Evolution of the Oxidation State and Structure by Oxidation of Subnanometer Cobalt Clusters

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• 作者：Chunrong Yin ; Fan Zheng ; Sungsik Lee ; Jinghua Guo ; Wei-Cheng Wang ; Gihan Kwon ; Viktor Vajda ; Hsien-Hau Wang ; Byeongdu Lee ; Janae DeBartolo ; S枚nke Seifert ; Randall E. Winans ; Stefan Vajda
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：September 18, 2014
• 年：2014
• 卷：118
• 期：37
• 页码：8477-8484
• 全文大小：405K
• ISSN：1520-5215

文摘

Size-selected subnanometer cobalt clusters with 4, 7, and 27 cobalt atoms supported on amorphous alumina and ultrananocrystalline diamond (UNCD) surfaces were oxidized after exposure to ambient air. Grazing incidence X-ray absorption near-edge spectroscopy (GIXANES) and near-edge X-ray absorption fine structure (NEXAFS) were used to characterize the clusters revealed a strong dependency of the oxidation state and structure of the clusters on the surface. A dominant Co²⁺ phase was identified in all samples. However, XANES analysis of cobalt clusters on UNCD showed that 鈭?0% fraction of a Co⁰ phase was identified for all three cluster sizes and about 30 and 12% fraction of a Co³⁺ phase in 4, 7, and 27 atom clusters, respectively. In the alumina-supported clusters, the dominating Co²⁺ component was attributed to a cobalt aluminate, indicative of a very strong binding to the support. NEXAFS showed that in addition to strong binding of the clusters to alumina, their structure to a great extent follows the tetrahedral morphology of the support. All supported clusters were found to be resistant to agglomeration when exposed to reactive gases at elevated temperatures and atmospheric pressure.